语法

static IEnumerable<string> T1()
{
    List<string> list = new List<string>();
    list.Add("a");
    list.Add("b");
    list.Add("c");
    return list;
}

Console.WriteLine("T1 start:");
foreach (var item in T1())
{
    Console.WriteLine(item);
}


static IEnumerable<string> T2()
{
    yield return "a";
    yield return "b";
    yield return "c";
}


Console.WriteLine("T2 start:");
foreach (var item in T2())
{
    Console.WriteLine(item);
}